1. Field of the Invention
The present invention relates to a shutter device of the split-blade type.
2. Description of Related Art
The mechanism of a focal plane shutter of the split-blade type is generally arranged as shown in FIGS. 38 to 40. Of these figures, FIG. 38 shows the shutter in a state having blades thereof ready to travel (a travel ready state). FIG. 39 shows the shutter in a state obtained while the blades are in process of making a slit exposure (a slit-exposure in-process state). FIG. 40 shows the shutter in a state obtained after completion of the travel of the blades (a travel completion state).
The focal plane shutter, which is shown in FIGS. 38 to 40 as a first example of the conventional arrangement, is composed of a shutter base plate 501 which is provided with a shutter aperture 501a, a first arm 504 and a second arm 505 which have their base end parts mounted on the shutter base plate 501 in such a way as to be swingable thereon, a slit forming blade 502 and covering blades 503, 512 and 513 which are rotatably connected to the first and second arms 504 and 505 and are arranged to open and close the shutter aperture 501a. A parallel link is formed by the first and second arms 504 and 505 in conjunction with each of the blades 502, 503, 512 and 513.
A second example of the conventional arrangement is a focal plane shutter disclosed in Japanese Laid-Open Utility Model Application No. SHO 52-84231. In the case of this shutter, a slit forming blade forms a parallel link in conjunction with first and second arms. One end of each covering blade is connected to one of the arms to be swingable thereon. The other end of each covering blade has either a working groove or slot or a working pin arranged to enable the covering blade to swing when the shutter is in operation.
A third example of the conventional arrangement is a focal plane shutter disclosed in Japanese Utility Model Publication No. SHO 53-21109. This shutter is arranged to support an arm by a blade group driving lever which is supported by a base plate having a shutter aperture. One end of the arm is connected to a slit forming blade in a swingable manner. A groove (or slot) part is arranged to guide the other end of the arm and the slit forming blade in such a way as to cause the slit forming blade to move in parallel when the blade group driving lever swings. The focal plane shutter is thus arranged to permit a reduction in size of the shutter.
In cases where a reduction in size (particularly in width) of a shutter is desired, it is advantageous in general to have a fewer number of split blades, because the number of connection parts whereby the blades are connected to arms becomes fewer accordingly. Thus, the use of a fewer number of blades lessens an area to be occupied by the connection parts. However, if the number of shutter blades is too few, the amount of mutual overlapping of the blades necessary for blocking a shutter aperture from light would become insufficient and, therefore, it is difficult to ensure an adequate light-blocking effect.
In respect of this point, the first example of the conventional arrangement does not allow much latitude in determining a position where the covering blades are to be connected to the arms. It is, therefore, difficult to increase the amount of mutual overlapping of the slit forming blade and the covering blade in a state of having them spread to close the shutter aperture.
In the case of the second example of the conventional arrangement, the covering blade is caused to make a swinging or revolving motion while the shutter is in process of shifting from a state of opening the shutter aperture and a state of closing the shutter aperture. This motion increases a difference in locus of motion between the covering blade and the slit forming blade which move in parallel with each other. Therefore, in order to efficiently attain a light-blocking effect (to uniform the amount of mutual overlapping of the blades in process of moving or spreading), the blades must be arranged to have complex shapes. In addition to this problem, inertia of the blades increases as the blades unnecessarily overlap in the neighborhood of the center of rotation of the covering blade which makes a swinging motion. The increased inertia becomes an impediment to a high-speed travel of the blades.
Shutter blades are generally arranged to be folded together in a space of a rectangular shape before opening the shutter. The rectangular space arrangement permits efficient use of space. However, the blades in the second example of the conventional arrangement are in a complex shape. In the case of the second example, therefore, the shape of the blade folding space deviates from such a rectangular shape, thereby preventing efficient use of space, and thus prevents the shutter from being arranged to be compact and yet to be adequately shielded from light.
In the third example of the conventional arrangement, a parallel moving mechanism including a guide groove (slot) and a guide pin, which has a larger working resistance than the parallel link of the first example, is used for the slit forming blade which has the longest distance from the center of swing and the longest moving distance among the blades. Therefore, it is difficult to ensure a smooth action of the shutter.
In view of the problems of the prior art, it is a first object of the invention to provide a shutter device arranged to permit a reduction in size, particularly in width, of the shutter device, and yet to effectively prevent degradation of a light-blocking effect by ensuring an adequate amount of mutual overlapping of blades in their spread state without impairing the smoothness of motion of the blades.
It is a second object of the invention to provide a brake mechanism arranged for a shutter device to be capable of minimizing heat generation without increasing the number of necessary parts.
To attain the above objects, in accordance with an aspect of the invention, there is provided a shutter device, which comprises a shutter base plate having an aperture part and a protruding part, a first shutter blade member arranged to travel a predetermined movement distance over the aperture part, a second shutter blade member arranged to travel a movement distance shorter than the predetermined movement distance of travel of the first shutter blade member over the aperture part, the second shutter blade member having a slot engaging the protruding part, a first arm member having one end part thereof pivotally supported by the shutter base plate and another end part thereof supporting the first shutter blade member in a swingable manner, and a second arm member having one end part thereof pivotally supported by the shutter base plate and another end part thereof supporting the first shutter blade member in a swingable manner, the second arm member being connected to the second shutter blade member, wherein the first shutter blade member and the second shutter blade member are caused to travel over the aperture part by the second arm member being driven.
In particular, in the shutter device, a connecting part of the second arm member where the second arm member is connected to the second shutter blade member is located between the one end part and the other end part of the second arm member.
Further, in the shutter device, the first shutter blade member includes a plurality of blade members.
Further, in the shutter device, the slot is formed in a curved shape.
Further, in the shutter device, the slot has such a shape as to impart a predetermined frictional force to the second shutter blade member in the middle of travel of the second shutter blade member.
Further, in the shutter device, a part of the second shutter blade member having the slot formed therein has a greater strength than a part of the second shutter blade member arranged to travel over the aperture part.
Further, in the shutter device, the part of the second shutter blade member having the slot formed therein is thicker than the part of the second shutter blade member arranged to travel over the aperture part.
Further, in the shutter device, the second shutter blade member has a greater strength than the first shutter blade member.
The shutter device further comprises an imparting member arranged to impart a braking force to the second shutter blade member in the middle of travel of the second shutter blade member.
Further, in the shutter device, the first shutter blade member and the second shutter blade member are in such oblong shapes that longitudinally extend in a direction perpendicular to a travel direction thereof, and are always parallel with each other with respect to the longitudinal direction.
Further, the shutter device is a focal plane shutter disposed in an image plane position.
In accordance with another aspect of the invention, there is provided a shutter device, which comprises a shutter base plate having an aperture part, a first shutter blade member arranged to travel a predetermined movement distance over the aperture part, a second shutter blade member arranged to travel a movement distance shorter than the predetermined movement distance of travel of the first shutter blade member over the aperture part, the first shutter blade member and the second shutter blade member traveling over the aperture part in a state of being linked to each other, and imparting means for imparting a braking action to the second shutter blade member in the middle of travel of the second shutter blade member.
Further, in the shutter device, the shutter base plate is provided with a protruding part, and the second shutter blade member is provided with a slot engaging the protruding part.
Further, in the shutter device, the slot is formed in such a shape as to impart the braking action to the second shutter blade member in the middle of travel of the second shutter blade member.
The shutter device further comprises a first arm member having one end part thereof pivotally supported by the shutter base plate and another end part thereof supporting the first shutter blade member in a swingable manner, and a second arm member having one end part thereof pivotally supported by the shutter base plate and another end part thereof supporting the first shutter blade member in a swingable manner, the second arm member being connected to the second shutter blade member, wherein the first shutter blade member and the second shutter blade member are caused to travel over the aperture part by the second arm member being driven.
Further, in the shutter device, the first shutter blade member and the second shutter blade member are in such oblong shapes that longitudinal extend in a direction perpendicular to a travel direction thereof, and are parallel with each other with respect to the longitudinal direction at least at a travel starting position or a travel ending position.